>>>>> [Function]
>>>>> For now we have to live with different meanings
>>>>> of _function_ when talking about databases:
>>>>> "The function of this function is to get the tuples from B
>>>>> that are functionally dependant on A."

>
>
>>>>> Three different contexts, but just about the same meaning:
>>>>>
>>>>> 1. General
>>>>> A purpose or use.
>>>>>
>>>>> 2. Math
>>>>> A binary mathematical relation over two sets D and C that associates
>>>>> with each element in D exactly one element in C.
>>>>> Set D is called the domain of the function, C its codomain.

>
>
>>>>> In both the math and software context, there is a sense of
>>>>> direction from domain (input) to codomain (output).
>>>>> For most purposes, this intuitive picture is good enough:
>>>>>
>>>>> |------------|
>>>>> --- x ---- >| f-machine |------ f(x) ----- >
>>>>> |------------|
>>>>>
>>>>> Where x is input in the "f-machine" and f(x) is output.

>>
>> Fair.
>>

>>>>>
>>>>> notes:
>>>>> every operator is a function
>>>>> every function is a relation

>>
>> Yes.

>
> Technically, in the standard vocabularies, every operator is a symbol
> not a function.